Nature: Natural spectacle in the Allgäu: purple bacteria color ponds

Natural spectacle in the Allgäu: purple bacteria color ponds

The water of the gypsum quarry pond is colored purple. The reason for the color is bacteria that bloom in the sulphur-containing water. photo

© Karl-Josef Hildenbrand/dpa

Lakes can shine in many different colors. But they rarely shimmer purple. But it does happen under certain conditions, as a Bavarian pond is currently proving.

A lake colored in shades of purple is currently an attraction in Ostallgäu. The so-called gypsum marsh near Füssen is discolored by bacteria. The spectacle can usually only be seen every few years; most recently, the pond was discolored by purple bacteria in 2020.

The prerequisite for the bacteria to appear is that there is little oxygen and sulfur in the water, explained the head of the water management office in Kempten, Karl Schindele, on Wednesday. “The bacteria are usually further down in the water, so you can’t see them.” Under certain conditions they would come to the surface. Temperature, wind and exposure to light would influence the discoloration. In this respect, it is not possible to predict how long the natural spectacle will last.

A number of interested people had already made their way to the lake in the past few days. Schindele does not see a health risk for humans or animals. In contrast to blue-green algae, which also occurs again and again When lakes form, the purple bacteria do not produce any toxins, he said. At the moment no one would probably go swimming in the pond because it’s not in season and the water smells of sulfur. He also doesn’t assume that dogs who like to drink from water can get sick. “Of course they don’t like the water either.”


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